Column content is not shown

It is caused by small column width and bug in TCPDF library. When column content overflows the cell width and cannot be broken into more lines (for example long SKU or price), TCPDF generator displays this column blank.
Solution is to make column wider. Go to Template edit, find Table Header and switch to HTML mode. Now add more % to desired column. Don't worry about other cell widths, they are recomputed in invoice to make 100%. Now switch editor back to design mode (Joomla! sometimes doesn' save editor if is in HTML mode) and save the configuration.  You don't need to change Table row width, only Header is taken info consideration.